Settling device for a fluid containing liquid, gas and particulate material, as well as a cleaning device provided herewith and a method for cleaning waste water

ABSTRACT

A settling device (2) for a fluid containing liquid, gas and particulate material comprises liquid-discharge elements (15) fitted close to the water level of the fluid and supply elements for supplying the fluid at the bottom of the settling chamber. In the settling chamber one or more caps (12) are disposed with their longitudinal axis at an angle to the water level, such that fluid supplied at the bottom of the settling chamber flows obliquely up, forced along the bottom of the at least one cap. Whilst gas bubbles contained therein collect in the ridge (17) of the at least one cap. The gas collected in the ridge of the at least one cap is trapped by elements (18) beneath the water level of the fluid. Preferably, use is made of a row containing a multiplicity of caps (12) which are disposed in oblique, overlapping and parallel arrangement. The caps (12) can be fitted at an angle of 60° relative to the water level and preferably have a mutual interval of about 6 cm. The invention further relates to a purifier provided with a settling device of this kind and to a method for the anaerobic purification of waste water using a settling device or purifier according to the invention.

FIELD OF THE INVENTION

The present invention relates to a settling device for a fluidcontaining liquid, gas and particulate material, comprising:

a settling chamber which is to be filled with this fluid and in whichthere is fitted, for the trapping of gas bubbles, at least one caphaving a ridge situated opposite a downwardly directed open side,

liquid-discharge means fitted close to the water level of the fluid,

supply means for supplying the fluid at the bottom of the settlingchamber, and

gas-discharge means for discharging from the settling chamber gas whichhas been trapped beneath the cap.

BACKGROUND OF THE INVENTION

A settling device of this kind is known from EP-A1-0,244,029 andEP-A1-0,193,999. These publications describe caps which are fittedhorizontally in overlapping connection and which are fitted to limit thetop edge of a fermentation chamber so as to form a settling chamberabove it. The caps trap gas bubbles rising from the fermentationchamber, whilst transfer of remaining fluid in the upward directionbetween the caps is permitted. The trapping of gas bubbles ensures thatthe fluid in the settling chamber is relatively still relative to thefluid in the fermentation chamber, the latter fluid being in a state ofmotion as a result of the rising gas bubbles. The fact that the fluidpresent in the settling chamber is relatively still means that particleswhich are present therein and have been carried along from thefermentation chamber are able to settle, these particles being able tofall back between the caps to the fermentation chamber. The settlingdevices known from these publications have the drawback, however, that,when major turbulences occur, bubbles can easily be passed between thecaps and then make their way into the settling chamber, thereby havingan adverse effect upon the settling in the settling chamber. Smaller gasbubbles, in particular will slip through easily between the caps.

The object of the present invention is, inter alia, to eliminate theabove-mentioned drawbacks.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a settlingdevice in which a liquid, gas and particulate material can be separated,such that at the top of the settling device a liquid is collected whichis largely free from particulate material and also, preferably, gas.

This object is achieved according to the invention by the fact that theat least one cap is disposed with its longitudinal axis at an angle tothe water level, such that fluid supplied at the bottom of the settlingchamber flows obliquely up, forced along the bottom of the at least onecap, whilst gas bubbles contained therein collect in the ridge of the atleast one cap, and by the fact that the gas-discharge means trap belowthe water level the gas collected in the ridge of the at least one cap.

Since fluid is supplied at the bottom of the settling chamber and liquidis discharged at the top of the settling chamber, an upward flow offluid will be generated in the settling chamber. The obliquely placedcaps ensure that this upward flow follows an oblique course. During thisoblique upward flow of fluid, the gas bubbles present therein will rise,as a result of their climbing capacity, more steeply than the rest ofthe fluid and will finally come into contact with the obliquely placedcap. The obliquely placed cap subsequently permits a further upward gasflow in the direction of the ridge of the cap. As the fluid flowsobliquely upward, the gas bubbles contained therein are thus collectedin the ridge of the cap. By trapping the gas collected in the ridge ofthe cap below the water level, this gas is prevented from setting inmotion the fluid at the water level. The fluid at the top of thesettling chamber will then be in a relatively still state, so thatparticles still contained in the fluid are deposited here more easily.By an obliquely placed cap should here be understood a body whoselongitudinal axis, for the purpose of the oblique placement, runs at anangle to the water level (or horizontal) and whose bottom side, viewedin a direction perpendicular to the longitudinal axis, the so-calledtransverse direction, for the purpose of forming a cap, likewise runs atan angle to the water level (or horizontal). The ridge of the cap is inthis case situated on the high side of the bottom side angled obliquelyin the transverse direction.

A further advantage of the settling device according to the invention isthat underneath the obliquely placed cap a laminar flow can be realized,which promotes the deposition of particles contained in the fluid. Thislaminar flow is particularly able to be realized by the fact that thegas bubbles which disrupt the laminar flow, such as described above, areseparated from the fluid and are separately discharged.

It is here pointed out that so-called oblique-plate settling devices areknown from the prior art, in which use is made of a number of flatplates placed obliquely in overlapping connection. In such plates, thebottom side, viewed in a direction perpendicular to the longitudinalaxis (i.e. in the direction of the transverse axis of the plate), runsparallel to the water level (or horizontal). Such oblique-plate settlingdevices are suitable for the treatment of fluids containing liquid andparticles. If these fluids contain gas bubbles, however, these gasbubbles will lend additional motion to the fluid flowing along theplates, thereby discouraging particles contained in these fluids fromsettling and disrupting any laminar flow.

According to an advantageous embodiment, the settling device accordingto the invention comprises a row containing a multiplicity of caps whichare disposed in oblique, overlapping and parallel arrangement. The fluidwill then be forced to flow upward via the interspaces formed betweenthe adjacent, overlapping caps. As a result of the multiplicity of caps,gas contained in the fluid will enter more rapidly into contact with aplate and will subsequently be collected in a ridge, so that thedisruptive influence of these gas bubbles upon the deposition ofparticles will be quicker to decline.

The trapping and discharge of gas collected in the ridge(s) can berealized in a variety of ways. For this purpose, use can be made, forexample, of an inverted funnel-like element fitted in the ridge on theinner side of the cap. The narrow outlet of the funnel can in this casebe connected to a pipe extending, for example, obliquely upward alongthe ridge, in order to discharge the gas upward via a separate duct,thereby preventing fluid close to the water level from being disturbed.According to an advantageous embodiment of the invention, thegas-discharge means can comprise a collecting pipe which extendsessentially horizontally through the ridges and which on the inner sideof the caps, close to the ridges, is provided with gas inlets having,for example, inverted funnel-like elements. According to anotherembodiment of simple design, the gas-discharge means can comprise acollecting cap extending essentially horizontally through the ridges.Such a collecting cap, which can match the oblique caps in terms ofshape, will generally have a smaller width than the obliquely fittedcaps. An advantage of a horizontally extending collecting pipe orcollecting cap is, inter alia, that the collecting pipe or collectingcap can simultaneously serve for the suspension and mutual positioningof the oblique caps in the settling chamber. Where a collecting capwhich extends through the ridges is used, it is also possible to collectand discharge floatable particles in a simple manner. By disposing theessentially horizontally extending collecting pipe or collecting cap ata slight angle of inclination relative to the water level or horizontalthe discharge of gas collected therein and any floating particles ispromoted.

The oblique caps of the settling device according to the invention willgenerally be fitted at an angle of 30° to 80° to the horizontal.Preferably, this angle will measure 55° to 65°. If the angle is toolarge, the gas bubbles contained in the fluid will be insufficientlytrapped by the caps. If the angle is too small, an upward flow isexcessively hindered. The value which is admissible for this angle willlargely depend upon the process conditions and the composition of thefluid to be treated. An angle of about 55°to 65°, such as, for example,an angle of about 60°, has been shown to produce good results underdiverse process conditions and with respect to diverse compositions ofthe fluid to be treated.

According to an advantageous embodiment, the caps are essentiallyV-shaped in cross-section, the angle between the legs of the V beingable to measure about 100° to 130°, preferably about 110° to 120°. SuchV-shaped caps are simple to produce by two plates being fastenedtogether or by a plate being folded at a suitable angle.

A laminar flow between the caps, in which particles present in the fluidcan easily be settled, can be realized according to the invention wherethe caps are fitted at mutual horizontal intervals of about 2 to 8 cm,preferably about 6 cm.

The invention further relates to a purifier for, for example, theanaerobic purification of waste water, comprising:

a fermentation chamber,

a settling device according to the invention, which is fitted above thefermentation chamber,

a degassing chamber, which is situated next to the settling device andwhich is divided by a partition into a first, relatively gas-richcompartment and a second, relatively gas-starved compartment, bothcompartments being interlinked at the top side of the partition and thedegassing chamber being here provided with a gas discharge, thegas-rich, first compartment being linked to the fermentation chamber andthe gas-starved, second compartment opening out into the bottom of thesettling chamber of the settling device, and

separating means fitted between the fermentation chamber and thesettling chamber of the settling device, which separating means trap gasbubbles rising in the fermentation chamber and discharge them to thefirst compartment of the gas-collecting chamber and conduct particlesdeposited in the settling chamber back to the fermentation chamber.

In the fermentation chamber there is sludge, which cleans waste watersupplied in an anaerobic environment to the fermentation chamber. Risinggas bubbles are thereby produced, which set the fluid in thefermentation chamber into violent motion, whereupon sludge particles andother particles swirl through the fluid. The gas bubbles are trapped bythe separating means and led away to the first compartment of adegassing chamber linked to the fermentation chamber. The gas bubbleswill rise up in this first compartment and, as a result of the highgas-bubble concentration, produce an upward flow of fluid in this firstcompartment. At the top of the degassing chamber, gas is able to escapefrom the fluid and larger, floatable particles will continue to floatout of the fluid. The escaped gas and the floating particles can then bedischarged, after which a fluid remains which is poorer in gas andparticles. This fluid, which is poorer in gas and particles, issubsequently conducted onward via a second compartment so as to reachthe bottom of the settling chamber of the settling device. The fact thatthe fluid undergoes a downward motion as it is conducted through thesecond compartment means that a portion of the gas bubbles which arestill being transported can flow back in the opposite direction so as toescape from the fluid at the top of the degassing chamber and be able tobe discharged. The fluid is subsequently conducted via the settlingdevice already described above, whereupon gas which still remains isfurther able to escape and particles which are still present are able tobe deposited from the fluid. The deposited particles fall back to thebottom of the settling device and make their way onto the separatingmeans between the fermentation chamber and the settling chamber. Fromhere, the deposited particles can be led back to the fermentationchamber. Using such a purifier, waste water such as waste water frombreweries, for example, or sludge-containing waste water, can be verywell cleaned. Various sorts of bacteria and supports therefor can beadded to the fermentation chamber, depending upon the sort of wastewater. Biomass and/or sludge can be situated in the fermentation chamberfor the anaerobic or aerobic purification of the waste water. Inpurifiers of this kind, the escaping gas will usually comprise O₂, CO₂,H₂, either alone or in combination with each other or with other gases.

According to a very advantageous embodiment, the separating means hereincomprise essentially horizontally fitted gas caps, which are disposedside by side and so that they overlap somewhat with their bottom ends,such that there is a vertical gap between the bottom ends of theadjacent gas caps to enable the particles deposited in the settlingchamber to be conducted back to the fermentation chamber.

For the gas caps, a large number of gas caps known from the prior artcan be used. Reference should particularly be made to those gas capsfitted above a fermentation chamber which are known from European patentapplications EP-A1-0,193,999 and EP-A1-0,244,029 of the applicant, whichgas caps, by being referred to as part of the present application, areherein incorporated.

The invention further relates to a method for the anaerobic or aerobicpurification of waste water using a device according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail below with referenceto the appended drawing. A purifier according to the invention isillustrated by way of example in this drawing, in which:

FIG. 1 shows a diagrammatic view in perspective of a purifier accordingto the invention;

FIG. 2 shows a diagrammatic, partially exploded side view of FIG. 1;

FIG. 3 shows a cross-section according to the lines III--III in FIG. 2;

FIG. 4 shows a detail of FIG. 1, in which, however, the caps 12 arefitted in a different, alternative manner, and

FIG. 5 shows a diagrammatic representation of the path covered by arising gas bubble in the settling device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The figures show a cleaning device 1 according to the invention, moreparticularly provided with a settling device 2 according to theinvention.

The cleaning device comprises a reaction chamber, such as a fermentationchamber 3 above which there is fitted a settling device 2. Thefermentation chamber 3 and the settling device 2 are separated from eachother by means of separating caps 4 (shown in purely diagrammaticrepresentation), as known from EP-A1-0,244,029 and EP-A1-0,193,999(herein incorporated by reference). The cleaning device furthercomprises a degassing chamber 5 comprising a first compartment 6 and asecond compartment 7, which compartments are separated from each otherby an oblique partition 8. At the top side of this partition 8, thecompartments 6 and 7 pass into each other. At the top of the degassingchamber 5 there is provided a gas discharge 9 and a spray device 10 forspraying water with the aim of releasing gas bubbles attached tofloating particles from said particles. At the top of the degassingchamber, at the level of the water level 23, there is likewise provideda discharge (not represented) for floating particles.

The settling device 2 comprises a multiplicity of V-shaped caps 12,which are placed obliquely at an angle of 60° to the water level 11 ofthe fluid. Each cap 12 has a downwardly directed open side 13 and anopposing ridge 14. The angle β between the legs of the V-shaped cap heremeasures about 110°. At the top of the settling chamber of the settlingdevice there are fitted, close to the water level 11 of the fluid,liquid discharge means in the form of overflow holes 15. These overflowholes 15 form a connection to a drain 16. The horizontal interval Zbetween two adjacent oblique caps here measures about 6 cm. The obliquecaps 12 are positioned relative to each other by means of an essentiallyhorizontally extending, V-shaped collecting cap 17 and are suspended bymeans of those caps 17 in the settling chamber of the settling device.This collecting cap 17 extends through the ridges 14 of the row ofsuccessive, mutually partially overlapping caps 12. Just below the ridgeof the collecting cap 17, passages 18 are formed in the ridges of theoblique caps 14 for the conduction of, in particular, gaseous fluid. Thecollecting cap 17 is preferably inclined somewhat obliquely toward thedegassing chamber 5 and opens out into the degassing chamber 5. Gasescollected beneath the collecting cap 17 and floating particles are thendischarged automatically, as it were, to the degassing chamber.

In the example illustrated, the separating means 4 comprise a whole cap30 and two half caps 19 fitted next to the latter and in somewhatoverlapping arrangement. The bottom ends of the caps 30 and 19 arefitted so that they overlap in such a way that a vertical gap 20 is hereformed, which is delimited by the bottom end of the cap 19 situatedabove and the top face of the cap 18 situated below. Via this gap 20,particles and fluid are able to flow back to the fermentation chamber 3below it.

The above-described purifier functions, as a whole, as follows:

Present in the fermentation chamber 3, for example, are biomass,bacteria, support material for these, sludge and other particles. Wastewater is supplied to the fermentation chamber via means (not shown),preferably continuously. The waste water is cleaned by the bacteriaand/or other means located in the fermentation chamber, therebygenerating gas such as O₂, CO₂, H₂. This gas formation sets the fluid inthe fermentation chamber into violent motion, as a result of whichparticles located in the fermentation chamber start to float around. Therising gas bubbles are in large part trapped by the caps of theseparating means 4. As illustrated by the arrows 21 and 22, this trappedgas is conducted to the first compartment 6 of the degassing chamber 5.Here, the gas will further rise, thereby producing an upward flow offluid. Fluid from the fermentation chamber 3 will consequently be guidedupward, whereupon many particles contained in the fluid will be carriedalong. The larger gas bubbles will leave the fluid at the top of thedegassing chamber 5 and will be able to be discharged via a gasdischarge 9. Floatable particles which are carried along with the fluidout of the fermentation chamber 3 will end up floating on the waterlevel 23 at the top of the degassing chamber. These floating particlescan subsequently be discharged and gas bubbles attached thereto are ableto be released by means of the spray device 10.

As a result of the gas which rises from the fermentation chamber andfrom the separating means 4, the fluid, as is indicated by the arrow 24,will be transported further obliquely downward via the secondcompartment 7 to the bottom of the settling device 2. As it flowsdownward through the second compartment, a portion of the gas stillpresent in the fluid can rise as bubbles counter to the flow directionand collect at the top of the degassing chamber 5, so as then to bedischargeable via a gas discharge 9. As is represented by arrows 25, atthe bottom of the settling device 2 a portion of the fluid will flowback via the gaps 20 to the fermentation chamber, particles deposited inthe settling device 2 being able to be carried along. As is representedby arrows 26, another portion of the fluid will be forced to flow alongthe obliquely fitted caps 12, after which finally, at the top of thesettling device, fluid is discharged from the purifier via the overflowholes 15.

During this forced upward flowing of the fluid along the bottom of theobliquely fitted caps 12, a laminar flow will be formed in which heavierparticles still present in the fluid will be easily deposited. Those gasbubbles which are still present in the fluid and disrupt such a laminarflow and lighter, floatable particles will rise vertically, or in anyevent more steeply than the fluid itself, as a result of the upwardlifting force which is thereby encountered. These bubbles and lighterparticles are then forced into contact with an oblique face of a cap andwill be conducted by this oblique face of the cap in question to theridge 14 of the cap in question. Along the inner side of this ridge 14,the gas and the lighter particles will then rise further until beingtrapped by the gas-discharge means fitted below the water level 11, inthis case in the form of an essentially horizontally fitted collectingcap 17. The gas and the lighter particles collect in the collecting cap17 and flow via the openings 18 along the bottom of the collecting cap17 to the degassing chamber 5, where the gas can further be dischargedvia the gas discharge 9 and the lighter particles via the discharge forthese (not shown). The fluid above the collecting cap 17 is virtuallytotally rid of gas and lighter, floatable particles, thereby promotingthe further settling of heavier particles still contained in the fluid.The uppermost layer of the fluid in the settling device, i.e. the fluidlayer located close to the water level 11, will be very low in particlesfloating through it. This fluid, which is very low in particles, canfurther be discharged as purified fluid via the overflow holes 15 andthe discharge ducts 16.

It will be clear that the settling device according to the invention canbe used in a variety of ways. Use in connection with the purifier whichis here outlined is very advantageous, but by no means the only usageoption. It will additionally be clear that the direction in which thecap(s) 12 is (are) obliquely fitted may vary. That is to say, withreference to FIGS. 1 and 2, that the caps 12 can also incline obliquelyto the right instead of obliquely to the left, as represented), orobliquely to the front or obliquely to the rear, whilst, here too,variants lying therebetween are conceivable.

FIG. 4 shows a design variant of the settling device according to theinvention. The difference with FIGS. 1-3 is essentially that theobliquely placed caps 12 of FIGS. 1-3 are rotated by 180° relative totheir obliquely running longitudinal axes and, in FIG. 4, are indicatedas caps 12. The caps 112 lie with their longitudinal side edges insealing arrangement against the side walls 120 of the settling chamber2. Each cap 112 comprises, as it were, two open downward-facing sides113 and two ridges 114. The ridges 114 are in this case situated alongthe side walls 120 of the settling chamber. Instead of a V-shapedcollecting cap 17, in the case of each ridge 114 there is provided anoblique, essentially horizontally running plate 117, which is placedwith its top edge against the side wall 120 of the settling chamber 2.In the embodiment according to FIG. 4, each (V-shaped) cap 112 thusforms, as it were, two caps.

FIG. 5 shows, with reference to a detail of FIG. 4, the course of a gasbubble in the settling device according to the invention. In zone 121,the gas bubble rises essentially vertically until the gas bubble comesinto contact with the cap 112. In zone 122, the gas bubble is thenconducted along the bottom of the cap 112 to the ridge 114. Havingarrived in the ridge 114, the gas bubble is conducted along the bottomof the ridge 114 to the collecting cap 117 (zone 123) so as subsequentlyto be discharged via the collecting cap 117 (zone 124).

I claim:
 1. Settling device for a fluid containing liquid, gas andparticulate material, comprising:a settling chamber having a bottom andadapted to be filled with said fluid; liquid-discharge means disposedclose to the water level for discharging liquid from the settlingchamber; supply means for supplying the fluid at the bottom of thesettling chamber; a row of oblique caps each having a ridge situatedopposite a downwardly directed open side and extending in a longitudinaldirection of the cap, the row of caps being located in the settlingchamber and disposed in overlapping and parallel arrangement with theirlongitudinal axes at an angle to the horizontal, such that fluidsupplied at the bottom of the settling chamber flows obliquely up,forced along the underside of the oblique caps, and gas bubblescontained therein collect in the ridges of the oblique caps; gasdischarge means for trapping gas collected in the ridges of the obliquecaps, and for discharging said trapped gas from the settling chamber,said gas discharge means including a collecting cap extendingessentially horizontally through the ridges of the oblique caps, andsaid collecting cap being disposed below the water level.
 2. Thesettling device according to claim 1, wherein the collecting cap isdisposed at a slight angle of inclination relative to the horizontal. 3.The settling device according to claim 1, wherein the oblique caps aresuspended in the settling chamber and positioned relative to each otherby the collecting cap.
 4. The settling device according to claim 1,further comprising a passage formed just below the collecting cap in theridge of each oblique cap.
 5. The settling device according to claim 1,wherein the oblique caps extend above the water level.
 6. The settlingdevice according to claim 1, wherein the oblique caps are disposed atmutual horizontal intervals of 2 to 8 cm.
 7. The settling deviceaccording to claim 1, wherein the oblique caps are disposed at an angleof 30° to 80° to the horizontal.
 8. The settling device according toclaim 1, wherein the oblique caps are disposed at mutual horizontalintervals of about 6 cm, and at an angle of 55 to 65° to the horizontal.9. The settling device according to claim 1, wherein the oblique capsare essentially V-shaped in cross-section, and the angle between thelegs of the V measures about 100 to 130°.
 10. A purifier for the aerobicor anaerobic purification of waste water, comprising:a reaction chamber;a settling device positioned above the reaction chamber, said settlingdevice comprising: a settling chamber having a bottom and adapted to befilled with said fluid; liquid-discharge means disposed close to thewater level for discharging liquid from the settling chamber; supplymeans for supplying the fluid at the bottom of the settling chamber; arow of oblique caps each having a ridge situated opposite a downwardlydirected open side and extending in a longitudinal direction of the cap,the row of caps being located in the settling chamber and disposed inoverlapping and parallel arrangement with their longitudinal axes at anangle to the horizontal, such that fluid supplied at the bottom of thesettling chamber flows obliquely up, forced along the underside of theoblique caps, and gas bubbles contained therein collect in the ridges ofthe oblique caps; gas discharge means for trapping gas collected in theridges of the oblique caps, and for discharging said trapped gas fromthe settling chamber, said gas discharge means including a collectingcap extending essentially horizontally through the ridges of the obliquecaps, and said collecting cap being disposed below the water level; adegassing chamber situated next to the settling device, and divided by apartition into a first compartment and a second compartment, bothcompartments being fluidly interconnected at the top side of thepartition, said degassing chamber including a gas discharge, the firstcompartment fluidly communicating with the reaction chamber and thesecond compartment opening out into the bottom of the settling chamberof the settling device; and separating means positioned between thereaction chamber and the settling chamber, said separating meansstructured and arranged to trap gas bubbles rising in the reactionchamber and discharge them to the first compartment of the gascollecting chamber and conduct particles deposited in the settlingchamber back to the reaction chamber.
 11. The purifier according toclaim 10, wherein the separating means comprise essentially horizontallyfitted gas caps disposed side by side, said gas caps having overlappingbottom ends which define a vertical gap between the bottom ends of theadjacent gas caps for enabling particles deposited in the settlingchamber to be conducted back to the reaction chamber.
 12. The purifieraccording to claim 10, wherein the collecting cap has one of its endsextending into the degassing chamber.
 13. Method for the separation of afluid containing liquid, gas and particulate material,comprising:providing a settling device having a settling chamber with abottom; supplying fluid at the bottom of the settling chamber, saidsettling chamber having a row of oblique caps disposed therein, each caphaving a ridge situated opposite a downwardly directed open side andextending in a longitudinal direction of the cap, the row of caps beingdisposed in overlapping and parallel arrangement with their longitudinalaxes at an angle to the horizontal, such that fluid supplied at thebottom of the settling chamber flows obliquely up, forced along theunderside of the oblique caps; collecting gas bubbles in the ridges ofthe oblique caps; and discharging trapped gas from the settling chambervia gas discharge means including a collecting cap extending essentiallyhorizontally through the ridges of the oblique caps, said collecting capbeing disposed below the water level.
 14. Method for the anaerobicpurification of waste water, comprising:providing an anaerobicfermentation chamber; providing above the reaction chamber a settlingdevice having a settling device with a bottom; supplying the waste waterat the bottom of the settling chamber, said settling chamber having arow of oblique caps each having a ridge situated opposite a downwardlydirected open side and extending in a longitudinal direction of the cap,the row of caps being disposed in an overlapping and parallelarrangement with their longitudinal axes at an angle to the horizontal,such that waste water supplied at the bottom of the settling chamberflows obliquely up, forced along the underside of the oblique caps;providing a degassing chamber next to the settling device, saiddegassing chamber being divided by a partition into a first compartmentand a second compartment, both compartments being fluidly interconnectedat the top side of the partition, the degassing chamber including a gasdischarge, a first compartment fluidly communicating with thefermentation chamber and the second compartment opening out into thebottom of the settling chamber; providing gas discharge means fortrapping gas collected in the ridges of the oblique caps, said gasdischarge means including a collecting cap extending essentiallyhorizontally through the ridges of the oblique caps, said collecting capbeing disposed below the water level; and providing separating meanspositioned between the fermentation chamber and the settling chamber,said separating means trapping gas bubbles rising in the reactionchamber and discharging them to the first compartment, and conductingparticles deposited in the settling chamber back to the reactionchamber.